Optical elements that direct electromagnetic radiation (EMR) along an optical path inevitably introduce some aberrations in the wavefront of the EMR. Such aberrations will be referred to herein as wavefront error (WFE). WFE degrades the performance of components in the optical path that utilize the EMR in some manner, such as a focal plane array or other sensor. For this reason, optical elements are often polished or otherwise manufactured to extremely tight tolerances, in an effort to ensure the highest performance possible.
Unfortunately, there is a direct correlation between manufacturing high-quality optical elements and the corresponding costs of the optical elements; so, requirements for extremely tight tolerances substantially increase the costs of such optical elements. Moreover, even where optical elements are successfully manufactured to extremely tight tolerances, when assembled in an optical assembly with other optical elements, each optical element and mounting element may introduce relatively small WFEs that accumulate into a relatively substantial WFE. This is sometimes referred to as “tolerance stacking.” Also, in some circumstances, the optical materials themselves can exhibit inhomogeneity such that even if ground to an ideal surface, the optical element may still introduce some WFE. Finally, in some applications, the optical assembly may receive EMR that has passed through one or more upstream optical elements, such as a window pane, that may also introduce WFE independent of the optical assembly.